He studied medicine in Rouen and Paris, where he learned clinical education at several hospitals. He developed an interest in neurology, and his first important scientific work involved lesions of the plexus brachialis. He earned his medical doctorate at Paris in 1898.

Guillain was a prolific writer. In 1920 with his friend Jean Barré (1880-1967), he published a major work titled Travaux neurologiques de guerre, a book that described the two doctors' clinical experiences during wartime. He was a member of French, American and Japanese academies of science, and in 1949 was appointed commander of the Légion d'honneur. He died in Paris.